Combine the ricotta with the oregano, salt, and pepper. Blend together.
Pretreat a large baking dish with PAM or rub the bottom with some olive oil so it doesn't stick.
Rub the chicken with the garlic powder. Heat the oil in a large skillet over medium-high heat. Add the chicken and cook for 10 minutes per side. You'll be tempted to move the chicken around but don't for at least 7 minutes, then check to see that it's not burning. Turn it over and do the same on the other side. Place the chicken breasts, side by side, in a lorge baking dish and allow to cool.
Preheat the oven to 350°F.
Spoon 1/4 cup of the cheese mixture and 1/4 cup tomatoes onto each chicken breast. You can be liberal. Top each chicken breast with 1 slice mozzarella. Bake for 20 minutes, or until a thermometer inserted in the chicken registers 170°F.